Congo Red Molecules Research Articles

Mechanistic performance of organic pollutants removal from water using Zn/Al layered double hydroxides imprinted carbon composite

A lithe zinc-aluminium layered double hydroxides were imprinted on activated carbon and fabricated Zn/Al LDHs@C composite. The composite matrix was utilized for the removal of toxic Congo Red (CR), Acid Red 1 (AR1) and Reactive Red 2 (RR2) dyes from water. The Zn/Al LDHs@C composite was characterized by Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy Dispersive X-Ray Analysis (EDAX), Brunauer-Emmett-Teller (BET), Thermogravimetric analysis-Differential scanning calorimetry (TGA-DSC) and Powder X-ray diffraction (PXRD) analytical techniques. The adsorption process was evaluated by varying the parameters such as contact time, composite dosage, pH of the solution, initial dye concentration and interfering anions. The maximum adsorption of CR, AR1 and RR2 dyes on Zn/Al LDHs@C composite were 44.09, 48.37 and 49.52 mg/g, respectively. The enhanced adsorption efficiency of the composite might be due to the existence of binding forces such as electrostatic attraction of the layered double hydroxide, hydrogen bonding sites on the Zn/Al LDHs@C and the surface complexation phenomena of the composite with the dye molecules. The Freundlich isotherm model was fit superior at the saturation point, indicating the heterogeneous surface interaction. Thermodynamic studies recommend that the adsorption process was spontaneous and endothermic in nature. The adsorption-desorption studies of Zn/Al LDHs@C composite were achieved up to five successive cycles with high efficiency. The enhanced adsorption efficiency of the Zn/Al LDHs@C composite suggested that the fabricated composite was suitable for the removal of CR, AR1 and RR2 dye molecules from water than any other developed hybrids.

1D hierarchical CdS NPs/NiO NFs heterostructures with enhanced photocatalytic activity under visible light irradiation

One-dimensional (1D) hierarchically structured CdS nanoparticles (NPs)/NiO nanofibers (NFs) heterostructures with remarkable removal efficiency for diazo dye Congo red (CR) were fabricated by a stepwise synthesis process, which was involved a chemical bathing deposition combined with calcination, and a microwave-assisted wet chemical reaction. The crystal phases, morphologies, optical absorption properties, and adsorption/photocatalytic activity of as-prepared products were investigated by XRD, FESEM, TEM, high-resolution TEM (HRTEM), N2 adsorption/desorption isotherms, UV–Vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectrum respectively. The experimental results indicated that binary satellite- core CdS NPs/NiO NFs heterojunctions are comprised of n-type CdS NPs with size of 10–30 nm decorated onto 1D p-type NiO NFs with diameter of 60–180 nm and length up to microns, which are self-assembled by nanoparticles with 30–100 nm in size. The possible formation mechanism for satellite-core structured CdS/NiO heterojunction is proposed. Interestingly, the decolorization efficiency over CdS/NiO heterostructures reached up to 91.2% in removal of aqueous CR at high concentration within 40 min under visible light irradiation, which was approximately 5.2 and 3.8 times as high as that of pure CdS nanocrystals (NCs) and the mixture of NiO NFs and CdS NCs. Furthermore, the possible photocatalytic mechanism was also investigated. The as-designed hybrid CdS NPs/NiO NFs heterostructures exhibited improved photocatalytic activity, which is attributed to the enhancement of the visible light adsorption, the efficient separation of photogenerated electrons and holes, and the high adsorption capacity towards CR molecules, thereby displaying superior visible- light-driven photodegradation of CR in high concentration. This work may provide a green engineering heterojunction technology to develop the advanced multifunctional nanocomposites for their applications in wastewater purification.

Preparation and characterization of MCM-48/nickel oxide composite as an efficient and reusable catalyst for the assessment of photocatalytic activity.

Mesoporous silica (MCM-48) was synthesized and used as a catalyst for supporting the nickel oxide photocatalyst. The loading of nickel oxide on MCM-48 results in a considerable reduction in the bandgap energy to 2.4eV. MCM-48 was used as a catalyst and back-supporter for the nickel oxide to enhance its photocatalytic properties along with adsorption capacity. Therefore, the adsorption capacity of MCM-48/Ni2O3 was enhanced by 17.5% and 32.2% compared to Ni2O3 and MCM-48, respectively. Furthermore, the percentage of photocatalytic degradation was improved by approximately 68.2% relative to the free-standing Ni2O3. The MCM-48/Ni2O3 proved the chemisorption adsorption mechanism that happens in multilayer form through the heterogeneous surface. This through fixing such Ni2O3 particles over the nanoporous topography to provide more exposed hot adsorption and photocatalytic sites for the incident light photons. Therefore, supporting Ni2O3 catalytic particles onto MCM-48 produces a new category of photocatalytic systems with promising active centers for the efficient degradation of Congo red dye molecules.

Enhanced visible light activity of EuFeO3/TiO2 nanocomposites prepared by thermal treatment–hydrolysis precipitation method

The present paper aimed to, through combination of TiO2 and a rare earth ferrite and EuFeO3 nanoparticles, synthesize a new visible light active photocatalyst. The EuFeO3/TiO2 nanocomposites were synthesized by a thermal treatment approach, in combination with a hydrolysis precipitation processing. The influences of concentration of TiO2 nanoparticles on morphological, magnetic and structural properties of EuFeO3/TiO2 nanocomposites were examined by different characterization techniques. Moreover, the optical characteristic of the synthesized samples was evaluated by UV–visible diffuse reflectance spectrophotometry. The nanocomposites’ photocatalytic activity was also assessed under the visible light (λ > 400 nm), considering Congo red molecules degradation. Considerable degradation efficiency was observed (68% after 30 min), especially after using EuFeO3/TiO2 nanocomposites ratio of 1:0.5. The performed analysis revealed that EuFeO3/TiO2 (1:0.5) nanocomposite could be structured in a way that led to a considerable redshift in the onset of light absorption in comparison with that of pure TiO2. The constructed EuFeO3–TiO2 heterojunction caused a considerable increase in the photocatalytic degradation of the target pollutant, as a result of occurred diminished in electron–hole recombination.

Magnetically assisted coagulation using iron oxide nanoparticles-Leucaena leucocephala seeds’ extract to treat synthetic Congo red wastewater

This study focused on utilization of Leucaena leucocephala seeds’ extract and iron oxide nanoparticles (IONPs) under magnetic field to provide effective coagulation process. Leucaena seeds’ extract was obtained using 3 M NaCl solution as solvent at feed-to-solvent mass ratio of 1:20. IONPs were synthesized using co-precipitation method. The obtained IONPs were analyzed using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. Based on analysis results, the obtained IONPs were the agglomerate of Fe3O4 phase with average particle diameter of 14.6 nm. The extract and IONPs were used as natural coagulant at various pHs (3–12), coagulant dosages (4–40 mL extract/L), and IONPs concentrations (0.5–3 mg/mL extract) under external magnetic field. It was obtained that pH 3 was the best pH because positively charged Leucaena protein at pH 3 acts to neutralize negatively charged Congo red molecules. The highest removal was obtained at coagulant dosage of 20 mL/L, and further increase in dosage was decreasing the removal due to colloid re-stabilization effect. The variation of IONPs concentration did not give any effect on the %removal and sludge volume. However, further investigation using pseudo-second-order kinetic model showed that the increase in IONPs concentration gave increase to the kinetic constant, signifying faster settling kinetics. The best condition was obtained at pH 3, coagulant dosage 20 mL/L, and IONPs concentration of 3 mg/mL extract that gave 90% Congo red removal, 30 mL/L sludge volume, and 30 min settling time.

Hexagonal Ni(OH)2 nanosheets for stabilizing Pickering emulsion and Congo red adsorption

In this paper, hexagonal Ni(OH)2 nanosheets were prepared by hydrothermal method with nickel chloride hexahydrate as matrix and ammonia as precipitant. The lateral size of Ni(OH)2 nanosheets was about 100–250 nm. The structure of the Ni(OH)2 sheets was characterized by XRD, SEM, IR, TGA etc. Pickering emulsion was prepared by using Ni(OH)2 nanosheets as stabilizer and dichloromethane (DCM) as oil phase. Furthermore, the stability factors of Pickering emulsion and the adsorption of Congo red (CR) on interface particle layer were studied. The adsorption equilibrium of CR was analyzed by Langmuir adsorption model and Freundlich adsorption model, and the adsorption process was researched by pseudo-first-order kinetics and pseudo-second-order kinetics. Compared with Ni(OH)2 in the water phase, the Ni(OH)2 in interface particle layer exhibited a much higher adsorption capacity and a faster deposition rate. The adsorption mechanism of CR can be mainly attributed to electrostatic interaction between the positively charged interface particle layer and the anionic CR molecules. It can be expected that as a promising adsorbent for CR removal in water treatment, the Ni(OH)2 sheets in Pickering interface layer can provide a new strategy for dye adsorption.

Synthesis and characterization of poly(ethylene terephthalate) fibers grafted with N-(hydroxymethyl) acrylamide by free radical: its application in elimination of Congo red

In this study, firstly, N-(hydroxymethyl) acrylamide (HMAAm) was grafted on poly(ethylene terephthalate) fibers (PET) by utilizing benzoyl peroxide (Bz2O2) as an initiator. The alteration in graft percentage with the polymerization time, temperature, concentration of initiator and monomers were investigated. For grafting experiments, the optimum temperature, duration for grafting and initiator concentration were found be 85 °C, 4 h and 0.008 M, respectively, and the maximum grafting yield was determined to be 25% at these conditions. After grafting, the morphological and chemical changes on the grafted fibers were examined scanning electron microscopy and Fourier-transform infrared spectroscopy. The thermal properties of the obtained PET fibers were examined with differential scanning calorimeter analysis. In addition, the water absorption capacities of the grafted fibers obtained at optimal conditions were investigated and it was found the maximum percentage of water retention reached 56%. Removal of Congo red (CR) with the grafted fibers was performed using a batch process. The effects of different parameters such as pH, grafting yield of HMAAm, adsorption time and CR concentration on the sorption capacity of the grafted fibers were investigated. The optimal pH for adsorption of CR was found to be 2, and the adsorption process reached equilibrium in 4 h. The amount of adsorbed CR molecules increased with the increment in the grafting yield up to 17%, and the graft copolymers adsorbed CR with 5.62 mg/g efficiency when the initial CR concentration was 80 ppm. The PET-g-HMAAm fibers synthesized in this study can be obtained easily and inexpensively, and the constructed fibers could be used to remove ionic substance from aqueous solution.

Fabrication of Novel Al(OH)3/CuMnAl-Layered Double Hydroxide for Detoxification of Organic Contaminants from Aqueous Solution.

A novel lamellar Al(OH)3/CuMnAl-layered double hydroxide (LDH) nanocomposite was successfully synthesized via the hydrothermal method and tested as a highly efficient adsorbent for the removal of Congo red (CR) dye from aqueous solution. Structural, morphological, and spectroscopic characterization of the Al(OH)3/CuMnAl-LDH nanocomposite were studied by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, photoluminescence (PL) analysis, and UV–visible spectroscopy analysis techniques. The CR dye adsorption performance of the prepared materials increased with an increase in functionality. The adsorption capacity of the Al(OH)3/CuMnAl-LDH nanocomposite (172 mg/g, pH 7, temp 30 °C) was found to be higher than that of pure Al(OH)3 (32 mg/g, pH 7, temp 30 °C) and CuMnAl-LDH (102 mg/g, pH 7, temp 30 °C). The results revealed that anion exchange and hydrogen bonding are mainly responsible for the adsorption of CR onto the Al(OH)3/CuMnAl-LDH nanocomposite. Moreover, the adsorption of CR in the presence of Cu(II) and NaCl salt showed a synergistic and antagonistic effect while the presence of anionic Cr(VI) ions had no significant effect. The adsorption thermodynamics, isotherm, and kinetics modeling analyses were also conducted to study the interactions between CR molecules and the Al(OH)3/CuMnAl-LDH nanocomposite. The adsorption of CR was found to be endothermic and followed by the pseudo-second-order kinetics and the Langmuir adsorption isotherm model. The developed nanocomposite showed excellent potential for treating industrial wastewater.

Modeling of CO<sub>2</sub>-Activated Adsorption on Chitosan Hydrogel for Dye Removal in Aqueous Solution

This work focuses on adsorption kinetics and isotherm modelling in CO2-activated chitosan. Removal efficiency and adsorption capacity were measured for three anionic dyes: Brilliant Blue FCF (BBF), Congo Red (CR), Orange II (O-II) and one cationic dye: Crystal Violet (CV). While the highest removal efficiencies of BBF, O-II and CR were 97%, 91% and 48%, it was found that very low adsorption capacity occurred in the case of CV due to the repulsion between the cationic groups of CV and that of CO2-activated chitosan. In terms of adsorption kinetics, pseudo-first-order and pseudo-second-order models were applied. The adsorption in the CO2-activated system was found to follow the pseudo-first-order model. The activation of adsorption by CO2 was found to lead to a higher adsorption rate constant and a higher adsorption capacity due to the protonation of chitosan’s amino groups. Interestingly, as the temperature of the CO2-activated system increased, the pseudo-first-order model predicted a decrease in adsorption rate constant, k1. This is thought to be a result of lower CO2 dissolution into the aqueous solution, which leads to a slower protonation process of chitosan’s adsorption sites. The chemical structure of the dye species affects the adsorption kinetics in the CO2-activated system. There are four charged functional groups on the CR molecule and three on the BBF molecule, which allow faster alignment onto adsorption sites compared with O-II molecules with only one charged group. In terms of adsorption isotherm, BBF adsorption was found to follow the Langmuir model in the CO2-activated system.

Construction of an electroneutral zinc incorporated polymer network nanocomposite membrane with enhanced selectivity for salt/dye separation

Electroneutral nanofiltration (NF) membranes are crucial to the treatment of textile wastewaters with high salinity, but it is challenging to generate electroneutral thin-film composite (TFC) membranes in a broad pH range. In this paper, we demonstrate the fabrication of an electroneutral NF composite membrane with the selective layer comprising of a zinc cation-integrated cross-linked polyvinyl alcohol (PVA)-polyethyleneimine (PEI) polymer network, which was deposited on an interlayer membrane of polydopamine-wrapped carbon nanotubes. The highly ionizable coordinative bonds formed between the Zn(II) ionic species and the amino groups in PEI facilitated ionization to generate hydrophilic and nearly electroneutral membranes with tenable electroneutrality over a broad pH range of 5.0–8.6. Subsequently, the membrane afforded excellent rejection (>99.7%) of bromothymol blue, congo red and direct yellow dye molecules while the low salt retentions of 3.35% (NaCl) and 11.57% (Na2SO4) were realized with moderately high water flux of up to 84 L m−2 h−1 at 5 bar. Further prolonged filtration of a salt/dye mixed feed system demonstrated that the salt presence did not affect the dye separation efficiency leading to the attainment of an unprecedented high NaCl/Congo red selectivity of 932. This highlighted the potentiality of the presented approach for designing membranes with tunable surface charges for the purification of saline textile wastewaters.

Feasibility of nanoscale zero-valent iron (nZVI) for enhanced biological treatment of organic dyes

Biodegradation of recalcitrant organic contaminants such as organic dyes is a fundamental challenge in wastewater treatment. We report herein the integration of nanoscale zero-valent iron (nZVI) with membrane bioreactors (nZVI-bio system) to achieve enhanced degradation of Congo red (CR) in wastewater. nZVI pretreatment converts the large and bio-recalcitrant CR molecules into smaller and more biodegradable organic compounds in continuous flow stirred tank reactors (CFSTR). A nZVI-bio system was experimented continuously for 52 d with a color removal efficiency of 99% and a reduction of chemical oxygen demand (COD) from 167 mg L−1 to less than 70 mg L−1. However, a conventional biotreatment system treating identical wastewater achieved color removal efficiency of just 30–70% and the COD reduction to 116 mg L−1. This suggests that integrated nZVI-bio system has potential for the treatment of recalcitrant organic dyes. On-line measurements of pH and redox potential in the CSFTR can be conveniently used to monitor and regulate treatment performance.

Adsorption Mechanism of Congo Red on Mg–Al-layered Double Hydroxide Nanocompound

In this work, congo red (CR) was removed by applying carbonate intercalated Mg-Al-layered double hydroxide (Mg-Al-LDH) nanocompound as an adsorbent. Batch adsorption experiments performed under various temperatures, ionic strengths, initial CR concentrations, alkalinities and shaking rates. The maximum adsorption capacities of Mg-Al-LDH for CR were 100, 105 and 86.8 mg g-1 at 308, 318 and 328 K, respectively. Adsorption sites of Mg-Al-LDH for CR were -OH groups attached to Al atoms of adsorbent layers. Adsorption isotherms of the process were studied by the ARIAN model and analysis of obtained data showed that there were two kinds of adsorption sites on the surface of Mg-Al-LDH. Results of instrumental analysis showed that these adsorption sites were -OH groups located on the surface of mesopores and micropores of adsorbent and were named MP and 003 sites, respectively. The kinetic data were studied by the KASRA model and ISO and intraparticle diffusion (pore-diffusion) equations which showed that CR molecules were adsorbed at first on the MP sites. Also, during the adsorption of CR on MP sites the interaction of CR with adsorbent surface was rate-controlling step. Furthermore, during CR adsorption on 003 sites, adsorption kinetics was diffusion-controlled.

Rapid in Situ Self‐Assembly of Carbon Fibers/ZIF‐8 Composite for Efficient Adsorption Enhancement of Congo Red

AbstractAlthough carbon fibers (CFs) are born with special physicochemical properties, the common CFs show the poor adsorption performance owing to the lack of adsorption sites and porosity with low specific surface area. As emerging functional materials, metal‐organic frameworks (MOFs) have attracted significant attention due to excellent properties, which has the ability of remedying drawbacks of other materials. In this study, zeolitic imidazolate framework‐8 (ZIF‐8) was rapidly coated on the surface of carbon fibers (CFs) (CF/ZIF‐8) via in‐situ self‐assembly approach in 10 min. The scanning electron microscope (SEM) images show ZIF‐8 film on CF is dense and homogeneous due to the low reactivity of zinc acetate and the coordination interaction between Zn2+ and carboxyl of CF treated by nitric acid (CF‐COOH). The Brunauer‐Emmett‐Teller (BET) surface area of CF/ZIF‐8 composite is about 30 times larger than that of pristine CF. The adsorption selectivity of CFs was increased after the modification of ZIF‐8 demonstrating by adsorbing different dyes. The CF/ZIF‐8 composites were applied to remove congo red (CR) from aqueous solutions with the adsorption capacity 40 times more than that of pristine CF and CF‐COOH, because of the increasing specific surface, electrostatic interaction and π‐π interaction between ZIF‐8 and CR molecule. The MOFs/CFs composites we fabricated also have great promise applications in micro‐preconcentration and electrochemistry.

Electric field endowing the conductive polyvinylidene fluoride (PVDF)-graphene oxide (GO)‑nickel (Ni) membrane with high-efficient performance for dye wastewater treatment

Due to potential toxicity of the dyes and their visibility even at the very low concentration, treatment of dye wastewater has been a matter of considerable interest. Membrane technology is an emerging technology that offers a promising way to remove dyes from wastewater. However, the membrane fouling and trade-off effect severely hinder the removal efficiency. In view of this, the conductive polyvinylidene fluoride (PVDF)-graphene oxide (GO)‑nickel (Ni) composite membrane was firstly developed and implanted into the dead-end filtration cell as the cathode in the sandwich-like electrode. Under the assistance of electric field, the conductive PVDF-GO-Ni membrane displayed 98.02% Congo red (CR) rejection with the flux of 38.39 L·m−2·h−1·bar−1, which was an encouraging result comparing to most previous reports. Moreover, PVDF-GO-Ni membrane possessed certain antibacterial ability and super anti-adhesion ability to CR molecules. The underlying mechanism of super anti-adhesion of CR molecules was investigated by quantitatively calculating the interfacial interaction energy according to the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. XDLVO theory indicated that the repulsive acid-based (AB) interaction energy between CR molecules and membrane surface predominantly facilitated the super anti-adhesion ability of the hydrophilic PVDF-GO-Ni membrane. The present study not only supplied a novel PVDF-GO-Ni membrane for high-efficient treatment of dye waste water, but also built an approach to quantitatively calculate interfacial interaction energy which should have a wide applications in forecasting and directing the modifications of separation membranes.

Amyloids, Congo red and the apple-green effect.

This paper attempts to find evidence of the previously proposed opinion that amyloids complex with Congo red molecules which preserve their supramolecular organization. As evidence of the overpowering tendency of Congo red molecules to self-assemble, we present an increasing acidity of molecules that follows increasing concentration of the dye, and a highly notable nonlinear increase in absorbance in the UV band (300-400 nm). This effect is analyzed in a model where the amyloid fibril is simulated by polyvinyl alcohol, providing a scaffold to stabilize a long Congo red micelle. Enormous absorbance in the UV band, coupled with the increasing association capabilities of individual Congo red molecules may cause the absorbance to extend even into the visible band. In addition, the UV and visual absorbance bands shift significantly, depending on conditions, and may either approach or recede from each other, leading to spectral changes which may be observed under polarized light. This commonly observed spectral variability appears to be associated with the strong capacity for electron delocalization in supramolecular Congo red complexed with amyloids.

Green fabrication of bentonite/chitosan@cobalt oxide composite (BE/CH@Co) of enhanced adsorption and advanced oxidation removal of Congo red dye and Cr (VI) from water

Bentonite/chitosan composite supported by green fabricated Co3O4 was successfully synthesized and its physicochemical properties were investigated utilizing several analytic techniques. The formation of the composite was confirmed by the XRD patterns, SEM, HRTEM images, and FT-IR analysis. The adsorption properties of bentonite/chitosan@Co3O4 for acidic dye (Congo red) and Cr(VI) ions were investigated. The kinetic studies reflected the saturation of the composite surface after 480 min for both Congo red molecules and Cr(VI) ions. Additionally, the systems are of chemisorption nature and showed excellent fitting with Pseudo-second order model. The mathematical parameters of the isotherm models revealed a monolayer uptake of Congo red molecules and Cr(VI) ions and represented mainly by the Langmuir model. The theoretical calculated maximum adsorption capacity (qmax) is 303 mg/g and 250 mg/g for Congo red molecules and Cr(VI) metal ions, respectively. The composite is of high reusability and can be used effectively for six runs of decontamination of Congo red molecules and Cr(VI) ions. Moreover, it is of high oxidation properties and can be used in the photocatalytic reduction of Congo red molecules and Cr(VI) ions from water. Besides that, bentonite/chitosan@Co3O4 green composite was used in purification of realistic water samples which make it one of the promising adsorbents.

Deconstruction of Pine Wood (Pinus sylvestris) Recalcitrant Structure Using Alkali Treatment for Enhancing Enzymatic Saccharification Evaluated by Congo Red

The changes of pine wood structure were evaluated based on Congo red (CR) adsorption in this study. Cellulose free –OH group act as electron acceptor and CR amino or azo group as electron donor that interacts each other to form H–bonds. This interaction of CR with cellulose is considered in this study to analyze the structural changes of pine wood. Pine wood samples were treated with different concentrated NaOH solution at 130 °C for 30 min. CR adsorption of treated samples were assayed in terms of absorbance decrease of CR solution measured by spectrophotometer. Field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) were used to evaluate the microstructural changes of treated samples. Finally enzymatic saccharification was carried out using commercial cellulase enzyme. Treatment of pine wood with alkali degrades the intra and/or intermolecular H– bonds of cellulose leading to an exposure of free –OH groups. These free –OH groups bind with CR molecule while in contact with CR solution. Structural change of pine wood caused by different NaOH (0 to 20%) treatment at 130 °C for 30 min was evaluated in terms of CR adsorption. Scanning electron microscopy and Fourier transform infrared spectroscopy studies showed that 10% NaOH treated sample exposed more cellulose fibers compared to other treatments leading to more CR binding. The cellulose crystalline index was increased with increasing NaOH–treatments and lowered by the 20% NaOH–treatment due to degradation of cellusose fibres. Moreover, after 72 h, reducing sugar yield was 76.5% and 70.7% using enzyme loading of 15FP U/g and 30CB U/g from 10% and 20% NaOH treated pine wood samples, respectively. Reducing sugar yield was decreased from samples while treating more than 10% NaOH solution. 10% NaOH treatment can be considered as an effective concentration for pine wood treatment at 130 °C for 30 min. These results suggest that CR approach is supposed to be helpful for selecting the treatment condition.

Hierarchical porous Al2O3@ZnO core-shell microfibres with excellent adsorption affinity for Congo red molecule

Three-dimensional hierarchical Al2O3@ZnO core-shell composite was designed and fabricated by a multistep strategy, involving an initial hydrothermal reaction, a subsequent chemical bath deposition process and a final calcination treatment. Electron microscopy images revealed that the Al2O3@ZnO composite was uniform in size and possessed a structure constituted by an Al2O3 core and a shell of crumpled ZnO nanosheets on which numerous pores were found. The as-synthesized Al2O3@ZnO core-shell composite exhibited fast kinetics and outstanding adsorption capacity for Congo red (CR) due to its unique structure and highly porous texture, which was much superior to those of bare Al2O3 core and ZnO microspheres. The pseudo-second-order kinetic model could represent the adsorption kinetics for CR adsorption, whereas the Langmuir isotherm model was suitable for describing the adsorption isotherm. The as-synthesized hierarchical Al2O3@ZnO microfibres with maximal adsorption capacity of 714 mg g−1 are highly competitive in terms of CR adsorption.

Removal of Congo red by thermally and chemically modified halloysite: equilibrium, FTIR spectroscopy, and mechanism studies

Unmodified halloysite and its heated and heat-processed/acid-leached forms were utilized for the adsorption of Congo red (CR) from aqueous medium. The samples were analyzed by ICP and nitrogen adsorption prior to the adsorption of the pollutant. We then studied the adsorption equilibrium of CR and the regenerating cycles of the most effective adsorbent. A special attention was paid to Fourier transform infrared analysis to elucidate the mechanism of CR adsorption onto halloysite materials. The thermochemical treatment results in the dehydroxylation of halloysite and an increase in SiO2 content. The modification increases specific surface area up to 503 against 63 m2 g−1 for unmodified halloysite. The Redlich–Peterson isotherm yields the best fit of the Congo red adsorption. The best adsorbent was found to be the heat-treated/acid-leached sample. It interacts with Congo red molecules through an outer-sphere complexation mechanism by implying silanol species and amino and sulfoxide groups. Understanding the interactions between pollutants and halloysite materials is an essential approach to improving the use of these clays in sewage treatment.

Ionic-Liquid-Controlled Two-Dimensional Monolayer Bi2MoO6 and Its Adsorption of Azo Molecules

Two-dimensional (2D) nanosheets with a single-layer thickness are currently an emerging field in synthetic chemistry. The preparation of these sheets is a challenge due to their predicted thermodynamic instability. Here, we determined that Bi2MoO6 nanosheets can be controlled by ionic liquids (ILs) with ammonium cation alkyl chain lengths and polar anions, and their adsorption capacities for azo molecules are in good agreement with the σ-profiles obtained from conductor-like screening models for realistic solvents. Particularly, monolayer Bi2MoO6 exhibits a superhigh adsorption capacity of 468 mg/g for Congo red (CR), and a molecular dynamics simulation reveals that the adsorption process has diffusion, association, and equilibrium steps. The interactions between the positively charged [BiO]+ groups on the surface of the monolayer Bi2MoO6 and the negatively charged center of CR molecules in aqueous solution are strong, leading to a large negative adsorption free energy of −81.8 kcal/mol. This work establishes a method to control the 2D monolayer and provides insight into the adsorption behavior.